1. Field of the Invention
The present invention relates to an method and a apparatus for roll surface machining to form a three-dimensional pattern of protrusions or recesses in the surface of a roll by using a cutting tool, and more particularly to a roll surface machining method and an apparatus for carrying out predetermined ultra-precision machining in the surface of a roll such as a roll mold for the production of, for example, an optical film for use in a liquid crystal display, a lenticular sheet for use in a rear projection TV, or a retroreflective sheet.
2. Background Art
A roll mold as described above has in the surface numerous fine protrusions or recesses on the order of several tens to several hundred μm. As described in Japanese Patent Laid-Open Publication No. 2004-344916, such a roll mold is produced, for example, by a method in which while rotating a roll and moving a cutting tool relative to the roll in the axial direction of the roll, the cutting tool is moved back and forth at a high speed in a cutting direction by means of a piezoelectric element, thereby forming circular or oval recesses in the roll surface, or a method in which grooves having inclined bottoms are machined at varying lead angles without moving a cutting tool in a cutting direction, thereby forming pyramidal protrusions in the roll surface.
In the production of such a roll mold, numerical control (NC) of the movements of the roll and a cutting tool is generally practiced. Because of the need for machining of the above-described large number of fine protrusions or recesses on the order of several tens to several hundred μm, huge volumes of data are needed for the numerical control. This necessitates using a high-capacity NC apparatus or taking measures, such as decreasing a roll diameter, to reduce the amount of data.